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CC&V has represented and demonstrated in the MLE Project Application that the mining of <br />• material on the surface of the diatreme will not, and can not, increase the concentration of <br />constituents in the regional ground water table that is intersected by the Carlton Tunnel. The <br />proposed mining will excavate a small proportion of the material in the diatreme, and will <br />somewhat increase the rate of oxidation of the contained sulfides in the mined material. These <br />sulfide materials will oxidize in the future, whether or not CC&V mines the rock containing <br />them. <br />a) DRMS had been observing peaks and valleys and a steady gradual increases in <br />sulfate concentrations in GW monitoring compliance wells in Arequa Gulch. <br />What does CC&V attribute the gradual rise in sulfate concentrations in these <br />compliance wells? Please explain. <br />Response. <br />CC&V does not have an explanation for the cyclic sulfate concentration in the Arequa Gulch <br />compliance wells. No similar behavior occurs in the regional ground water table intersected <br />by the Carlton Tunnel. CC&V is in the process of designing an investigation to evaluate the <br />behavior of water flowing in Arequa Gulch. However, it is noted that the entire Arequa <br />Gulch catchment area inside the mine boundary is to be covered with Phase 5 of the VLF, <br />which is expected to further eliminate any flow. <br />0V. The statement that the water quality will be similar to Carlton Tunnel water is of concern <br />on two levels: <br />a) First, these are two significantly different environments, one being an <br />underground flow system that has been flowing for decades and has established <br />some level of equilibrium as evidenced by the relatively consistent water quality <br />of the tunnel discharge, the other a pile of fresh, crushed rock that will be exposed <br />to a new environment of weathering and oxidizing conditions. It is unlikely the <br />two systems will weather and leach similarly. <br />b) The Carlton Tunnel has been there for over 60 years, and if an assumption is made <br />that the ground water flow system feeding it has established some kind of stasis or <br />equilibrium, then DRMS, wonders about the existence of preferential flow paths <br />causing selective dissolution and depletion of available minerals along those flow <br />paths. The overburden that will be crushed and piled will be fresh material and <br />has not undergone that level of selective dissolution and depletion. <br />Response: <br />CC&V has conducted a very extensive amount of testing of the sulfide oxidation behavior of <br />the materials to be mined in the MLE. The conclusion is that the neutralized leachate from <br />sulfide oxidation occurring in freshly broken material is the same as the neutralized leachate <br />from historic underground workings and other sources not associated with the current surface <br />• mining program. <br />Preferential pathways for flozu to and through the historic underground workings existed at <br />the time of the initiation of the current surface mining. As a result of the placement of <br />42